Generally, the present invention relates to a measuring instrument and, more particularly, to a scanning probe microscope with aligning function, the scanning probe microscope acting to detect the position of a certain foreign substance, crystal defect, or the like on a sample and to measure the shape at a subnanometer resolution.
Foreign matter-inspecting apparatuses using optical methods are available as instruments for inspecting foreign matter on a sample (generally, a wafer). Examples include WIS9000 manufactured by ESTEK Corporation and Surfscan 6200 manufactured by Tencor Corporation. Any of these instruments produces output signals indicating the size of the foreign matter and the position, or coordinates.
The prior art method of analyzing the shape of a foreign substance and making an elemental analysis of it is implemented by an apparatus which receives coordinates from the aforementioned foreign matter-inspecting apparatus, analyzes the shape of the foreign substance, and makes an elemental analysis of it with a scanning electron microscope (SEM) or the like. Examples of this apparatus include SAI9600 manufactured by Seiko Electronic Industries Corporation. Linkage of coordinates between the foreign matter-inspecting apparatus and the SEM is described in Patent Laid-Open No. 174644/1994.
Furthermore, an atomic force microscope or microscopy (AFM) has been proposed as an instrument capable of observing a sample at an atomic resolution. This AFM is disclosed, for example, in Patent Laid-Open No. 130202/1987. A method of aligning the probe of an AFM with the optical axis of an optical microscope is described in Patent Laid-Open No. 40356/1991. With this method, the distance (x.sub.1) between the probe and the optical axis of the optical microscope can be easily calculated. The AFM is equipped with a cantilever having a sharp protruding portion (probe) at its free end. When the probe is brought closer to the sample, the free end of the cantilever is displaced by the interaction (atomic force) exerted between the atoms at the front end of the probe and the atoms on the surface of the sample. The probe is scanned along the surface of the sample while measuring the displacement of the free end electrically or optically. In this way, three-dimensional information about the sample is obtained. For example, if the probe is scanned while controlling the distance between the probe and the sample in such a way that the displacement of the free end of the cantilever is kept constant, then the front end of the probe moves along the topography of the sample surface. Consequently, a three-dimensional image representing the surface topography of the sample can be obtained from the information about the position of the front end of the probe.
When a foreign substance is observed with an SEM, if the diameter of the foreign substance is less than 0.1 .mu.m, or if the height of the foreign substance is as low as several nanometers, then it is difficult to detect the foreign substance with the SEM. Especially, an element of the same species, e.g., a silicon foreign substance on a silicon wafer, is very difficult to observe with the SEM. Furthermore, it is difficult for the SEM to discern whether the foreign matter on the wafer is convex or concave. Where the coordinates are linked to the foreign matter-inspecting apparatus, the aligning accuracy is normally on the order of .+-.100 .mu.m. The possibility that a foreign substance of the order of 0.1 .mu.m is detected in a short time is very low.
On the other hand, the AFM makes a mechanical scan and so the scanning velocity is low. Furthermore, the maximum field of view is as narrow as 100 .mu.m. Therefore, the possibility that a foreign substance of the order of 0.1 .mu.m is detected is low, in the same way as in SEM. Since the problems described above occur, it is an object of the invention to solve these problems.